No amount of seniority can make someone a successful manager; a certain temperament and a host of personality traits are crucial to one's ability to lead. Harvard Business Review would argue that emotional intelligence, or the ability to "be aware of, control, and express one's emotions, and to handle interpersonal relationships judiciously and empathetically," is one of those critically important traits.
"The most effective leaders are all alike in one crucial way: They all have a high degree of what has come to be known as emotional intelligence," wrote Rutgers psychologist Daniel Goleman in one of HBR's most enduring articles, "What Makes a Leader?" "My research, along with other recent studies, clearly shows that emotional intelligence is the sine qua non of leadership. Without it, a person can have the best training in the world, an incisive, analytical mind, and an endless supply of smart ideas, but he still won't make a great leader."
More specifically, the broader term of EQ encapsulates five specific traits that allow individuals to "recognize, connect with, and learn from their own and other people's mental states." These include self-awareness, self-regulation, motivation (as defined as a passion for work that goes beyond money and status), empathy for others, and social skills, i.e. a proficiency for building and maintaining a professional network.
Beyond establishing the importance of emotional intelligence in shaping a person's ability to manage and lead, Harvard Business Review also developed a 25-question quiz designed to score a person's EQ. They recommend first responding to all 25 questions as honestly as possible, reflecting on your strengths and weaknesses once you get your score, and asking two trusted friends to evaluate you using the same statements. Other people's perspectives can help you to "learn whether your own insights match what others see in you," which is a key tenant of EQ.